1. Field of the Invention
The present invention relates to a system and method for changing communication channels, and more particularly to a system and method for changing communication channels which enables reliable data communication without communication interruption when a communication channel is changed to a direct channel or a relay channel according to a channel setting environment.
2. Description of the Related Art
Transmission of data from one terminal to another is performed using two main methods, one using a relay channel, the other using a direct channel.
In the relay channel communication method, a terminal which desires to transmit data (hereinafter, referred to as a “transmitting peer”) divides transmission data into a number of frames and sequentially transmits the frames to a relay server. The relay server then transmits the transmitted frames to a terminal which desires to receive data (hereinafter, referred to as a “receiving peer”).
On the other hand, in the relay channel communication method, a transmitting peer directly transmits frames produced through division of the transmission data to a receiving peer without passing through a relay server and thus the method is generally referred to as “Peer to Peer (P2P)”.
The direct channel communication method is considered an efficient communication method since it enables high data transmission speed while imposing little load on the relay server. However, the direct channel communication method cannot perform data communication when access to the receiving peer is not permitted due to firewall, Network Address Translator (NAT), or the like.
In one conventional method for overcoming this problem, the transmitting peer performs data communication with the receiving peer through a direct channel communication scheme when direct channel communication is possible between the transmitting peer and the receiving peer and performs data communication with the receiving peer through a relay channel communication scheme when direct channel communication is not possible (see Korean Registered Patent No. 0703065).
However, this conventional method has the following problems.
Data communication is performed after a communication channel is established. Therefore, when direct channel communication becomes impossible while data communication is being performed through the direct channel communication scheme, a communication channel should be reestablished to resume data communication, thereby reducing data communication continuity.
In the case where the conventional guaranteed reliability protocol is used, a list of frames that have not been successfully transmitted is newly generated and used for communication when a communication scheme has been changed. This increases data transmission time and reduces data transmission reliability.